Aircraft: SMALL TRANSPORT
Phase of flight: Initial Approach
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy

This report identifies potential human factors traps in the design of the ROZZE.ROZZE2 RNAV Arrival in MHT. They were observed during our flight into MHT. There were no known violations of FAA Regulations. The flight operated normally and safely. The following were observed: on the arrival; there are multiple fixes that begin with the same letter of the alphabet. This could potentially cause the crew to select the incorrect fix if cleared to one of these fixes to join and continue the RNAV arrival. I have noticed this on other RNAV arrivals; and it is a potential human factors trap. I suggest that each fix begin with a different letter of the alphabet; to avoid potential pitfalls in a high workload environment; such as when a crew is issued this arrival while already approaching the terminal environment; thus causing them to reconfigure the FMS automation. Note that fixes 'PNARD' and 'NUUKM' are overlaid upon each other; making it impossible to determine which fix applies to the transition to land south on Runway 17; via 'PURBL'; or Runway 24; via 'JSTNN'; or land to the north on Runways 6; via 'TEETO' or Runway 35; via 'SHOWZ'. Note that the notes for 'PURBL'; 'TESTO; and 'SHOWZ' indicate that the pilot may expect either RADAR VECTORS to the final approach course; reading the notes as written; it is easy; again from a human factors viewpoint; to read that the pilot can expect vectors for one of the approaches. However the intent of the note is that the pilot may be issued either RADAR VECTORS for the approach or; will be expected to fly a transition off of one of the fixes; 'PURBL'; 'JSTNN'; 'TEETO'; or 'SHOWZ'. Again; in a high workload environment; the intent of this wording may be easily misunderstood. The wording should include the phrase; 'expect to fly the transition for the respective approach; or RADAR VECTORS to the final approach course.' ATC verbal instructions should include the verbiage; 'after PURBL'; fly the ILS transition for the ILS 17 Approach.' However ATC may actually issue a clearance which very much sounds like a restatement of the clearance to fly the RNAV STAR; verbalizing only the expected runway transition on the STAR itself; such as 'ROZZE2; PURBL; ILS 17.' A pilot may easily interpret this as a clearance or re-clearance to fly the ROZZE2 RNAV with the transition for a landing to the south via 'PURBL' and then expect further instructions for one of the options listed; e.g. RADAR VECTORS to the approach; etc. Also; late issuance of the type of option to fly; e.g. RADAR VECTORS or the transition from the IAF listed on the approach plate; may cause a delay in sequencing the FMS logic in a timely manner. The following are a summary of suggestions to enhance clarification of RNAV STARS; specifically in this example; the ROZZE.ROZZE2 RNAV arrival into MHT: Each RNAV fix should begin with a different alphabet letter; no two fixes should begin with the same letter of the alphabet. RNAV fixes should be clearly delineated on the chart; fixes should not be overlaid so close that the transitions associated with them cannot be clearly identified and understood. Expectation instructions listed on the RNAV chart should be clearly written; e.g. 'Landing Runway 17; EXPECT to fly the ILS 17 transition; or; EXPECT RADAR VECTORS to the final approach course.' ATC instructions should clearly communicate the actions that the pilot is to take; e.g. 'after 'PURBL' fly the ILS transition to the ILS Runway 17 Approach' or; 'after 'PURBL' fly heading ### and expect RADAR VECTORS to the ILS 17 Approach.' Small Transport pilot reported alleged confusing and ambiguous arrival chart nomenclature and information during arrival to MHT.